Abstract The X chromosome coded `Methyl CpG binding protein 2' (MECP2) is highly expressed in neuronal tissues and named for its recognition of the methyl-CpG (mCpG) epigenetic modification. The importance of MeCP2 to neuronal and brain development is highlighted by the fact that MeCP2 mutations cause >90% of the diagnosed cases of the autism spectrum disorder Rett syndrome. Recent genomic studies have raised important questions regarding the full range of DNA sequences and types of base modifications bound by the protein. Our proposed studies seek to determine the molecular mechanisms underlying specific recognition of the type of nucleotide modification, DNA sequence, and binding cooperativity that meld to mediate localization of MeCP2 on chromatin. Our project interleaves energetic and structural analyses proposing quantitative assembly studies to determine the combinations of nucleotide modification with local and flanking DNA sequences that confer high specificity MeCP2 binding, the structure of MeCP2 - DNA complexes to reveal if differences exist among the bound target sites, and determine how MeCP2 competes with linker histones on chromatin and subsequently localizes to specific sites. Our proposal integrates established and novel quantitative and structural approaches to explore how binding of this key regulatory protein to chromatin initiates a cascade of molecular interactions that guides neuronal development.